As previously stated, the present invention is used with an artificial leg or prosthesis worn by an above knee amputee.
There are today about 50 different above knee prosthetic devices on the market. Many of these prostheses involve:
a socket for receiving and engaging the stump of the user; PA1 a knee bracket rigidly connected to the socket; PA1 a frame extending down from the bracket and being pivotally connected to the bracket by a horizontal shaft, said bracket, shaft and frame together combining to form an artificial knee joint; PA1 a pylon and artificial foot connected to the base of the frame; and PA1 means for controlling the knee joint by locking it to prevent it from buckling under load in the stance phase of a step, and freeing it in the swing phase of the step. PA1 separate means for variably damping or resisting each of flexion and extension rotational movements of the knee joint, said means preferably comprising a linear hydraulic damper adapted to simultaneously damp in both flexion and extension; PA1 electronic sensing means for measuring at least two AKP characteristics which vary with the activity of the AKP, preferably AKP knee angle and lower leg bending moment strain (which are respectively indicative of the angle between the leg segments and the position of the center of gravity of the user's body relative to the AKP foot) and emitting signals indicative thereof; actuating means, such as a servo motor, for adjusting the separate damping means to vary the resistance to rotation of the knee joint in at least one of flexion and extension; and programmed computer means for receiving the emitted signals from the sensing means, continuously establishing from said signals the state of the AKP in the course of a repetitive movement and activating the actuating means as required to vary damping to substantially simulate natural knee action. More particularly, the computer means is preferably adapted to do this by comparing the sensor signals to stored threshold values which are indicative of pre-determined transition points between states of the AKP in the course of a movement, and, when the received signal values correlate with stored values, then causing the actuating means to vary damper resistance as required so that the AKP knee joint action substantially simulates natural knee action. PA1 a hollow closed cylinder filled with hydraulic fluid and having a cylindrical hollow piston adapted to slide longitudinally within the cylinder chamber; PA1 the piston has axial rods extending from its ends, which rods project through sealed openings in the end walls of the cylinder. The piston further carries an exterior circumferential seal ring between its ends, for sealing against the side wall of the cylinder; PA1 a first aperture and check valve assembly, associated with a first end wall of the piston, enables fluid to enter the piston chamber from the first end of the cylinder chamber; PA1 a second aperture and check valve assembly, associated with the second end wall of the piston, allows fluid to enter the piston chamber from the second end of the cylinder chamber; PA1 a first pair of diametrically opposed ports extend through the piston side wall adjacent its first end, on one side of the seal ring; PA1 a second pair of diametrically opposed ports extend through the piston side wall adjacent its second end, on the other side of the seal ring; PA1 preferably, each first port is offset circumferentially from the second port on that side of the piston; PA1 preferably, each port is circumferential in position and slit-like in configuration; PA1 a valve preferably extends into the cylinder and piston chambers and is adapted to progressively reduce or increase the effective area of the first (or flexion) ports available for fluid flow and separately progressively reduce or increase the area of the second (or extension) ports; PA1 most preferably the valve comprises a rotatable shaft extending into the piston chamber in parallel relation to the cylinder axis, said shaft carrying a pair of radially protruding, diametrically opposed lobes, each lobe being adapted to substantially seal against the inside surface of the piston side wall, each lobe further being adapted, when the shaft is rotated, to progressively cover or uncover the adjacent flexion and extension ports, to thereby separately and simultaneously control flow area through the flexion and extension ports. PA1 If the valve is positioned to enable flexion and if the piston is forced downwardly, thereby pressurizing fluid in the lower end of the cylinder chamber, fluid will flow upwardly through the lower check valve and extension ports, if open, into the piston chamber and will leave the piston chamber through the upper flexion ports--fluid will not leave the piston chamber through the extension ports (if uncovered) because there is no significant fluid pressure differential between the lower end of the cylinder chamber and the piston chamber; PA1 If the valve is positioned to enable extension and if the piston is pulled upwardly, thereby pressurizing fluid in the upper end of the cylinder chamber, fluid will flow downwardly through the upper check valve and flexion ports, if open, into the piston chamber and will leave the piston chamber through the lower extension ports--again fluid will not leave the piston chamber through the flexion ports because there is no significant fluid pressure differential between the upper end of the cylinder chamber and the piston chamber. PA1 The valve can be adjusted to vary port areas and thus fluid flow rates to thereby vary resistance to knee joint rotation in either flexion or extension at the same time, thereby enabling variation of damping in both directions at the same time; PA1 Because the ports are "balanced" or provided in diametrically opposed pairs, the valve does not get pressed against one side of the piston wall under heavy load and therefore does not seize up or become difficult to move--thus a small motor and Shaft can be used to control the damper, which contributes; to the compactness and lightness of the unit; PA1 Because the damper is hydraulic, it is not significantly affected by wear and remains substantially consistent in its damping performance, thereby enabling the user to become accustomed to its "action" and to gain confidence in its performance. One could argue that the temperature of the hydraulic oil could vary and this would affect consistency of performance but this effect is minimized by using aircraft hydraulic fluid. PA1 a pair of closed chambers (for example the two ends of the cylinder chamber); PA1 means (for example the piston and cylinder) connected to the leg segments and forming two passageways (for example each formed by a check valve assembly, the piston chamber and a pair of the ports), for moving or circulating fluid from one end chamber to the other through one of the passageways when the leg segments are moving together and through the other of the passageways when the leg segments are moving apart; and PA1 means (for example the valve and port assembly) for regulating the flow of fluid through each passageway. PA1 storing, in a computer memory, threshold values of lower leg bending moment strain and knee angle, which values are indicative of the knee bending in stance phase, of anterior positioning of the center of gravity of body weight relative to the ankle or foot, and of swing phase, all in the course of a step along a level surface; PA1 continuously sensing lower leg bending moment strain and knee angle during use of the AKP and producing electronic signals corresponding thereto; PA1 comparing the signals against the stored threshold values and, when the signals substantially correlate with threshold values, actuating means for altering the rate of rotation of the knee joint in at least one of flexion and extension to enable the knee joint to flex at about the beginning of stance phase, to lock the knee joint against flexion while enabling extension in the middle portion of stance phase, and to free the knee joint as it approaches the swing phase thereby substantially simulating natural knee action; and PA1 repeating the foregoing repetitiously.
Now, the biological or natural knee joint is powered by the actions of muscles. Muscle has two elements. One is the active force developed by contraction and the other is variable stiffness. It has not been feasible to duplicate muscle contraction in leg prosthetics, due to limitations arising from weight and bulk. As a result, research has focused on implementing stiffness into the knee joint. This has usually involved switching the knee joint between one of two modes: locked up or free to rotate.
In recent years, researchers have sought improvement in controlling the action of the artificial knee joint, as a way to improve gait and enable the amputee to better deal with certain distinct actions, such as descending stairs or lowering into a sitting position.
A relevant patent in this regard is French patent 2623-086-A. This patent teaches providing a strain gage sensor on the frame between the knee joint and foot, to measure load. The electronic signals from the sensor are transmitted to a microprocessor which monitors the load measurement. When the load signal indicates that the swing phase of the step is ending and load is being applied to the leg, the microprocessor causes a motor or electromagnet to lock up the knee joint. When the stance phase is complete, the microprocessor instructs the actuator to release the knee joint, so that it is free to pivot in the swing phase.
Another relevant prior art reference is Russian patent SU1333-333-A. This patent teaches using a sensor at the knee hinge, to measure knee angle. Means lock or free the knee hinge in response to the knee angle measurements.
Another relevant prior art device is known as the Henschke Mauch S-N-S system for controlling an above knee prosthesis. This system incorporates a linear hydraulic damper for resisting rotation of the knee joint at a single damping rate in the stance phase. The damping rate can be varied by manual adjustment. When the knee joint is fully extended, the damper assumes a non-resisting mode. Otherwise stated, the system lacks automatic variation of damping and incorporates only two conditions, namely high resistance to flexion in stance phase and free rotation in swing phase.
If a knee joint is looked at as a simple hinge, there are two separate actions which can occur. In "flexion", the knee joint rotates to enable the upper and lower leg segments to move closer together. In "extension" the knee joint rotates in the opposite direction, the leg segments move apart and the leg straightens. For an artificial knee joint to more closely simulate a biological knee joint, it is necessary that control of resistance to knee rotation be applicable separately and variably in each of the flexion and extension modes. For example, it is desirable at the beginning of the stance (i.e. weight bearing) phase of the step to allow a small amount of knee flexion to occur and to then lock the knee against further downward flexion while simultaneously freeing the knee to extend as the leg straightens due to body action. So in the latter phase of this action, the knee joint is altered to being locked or stiff in flexion and free in extension, at the same time.
To applicant's knowledge, there is no artificial knee joint mechanism disclosed in the prior art which enables separate, simultaneous and automatic variable control of flexion and extension.
If such a mechanism could be devised, then a much more sophisticated control over the knee joint action could be implemented.
It is the object of the present invention to supply such a mechanism and to then incorporate it in an improved overall prosthesis.